CODEWITHSUNDEEP
pythonhash
Anin Smith
Anin Smith

Reputation: 103

Implement hashing function with collision

For a demo project, I want to create a hashing function with a very high probability of collision. Something simple is fine since the aim of the project is NOT security - but to demonstrate hash collisions.

Can anyone help me get started with an algorithm, or a sample implementation, or just point me in the right direction?

I am doing this in Python, though maybe that should not matter.

Upvotes: 1

Views: 315

Answers (2)

Antimony
Antimony

Reputation: 2240

One algorithm that comes to mind is hashing using the first letter of the string.

Something like 

hash[ord(text[0]) - ord('a')] = text

So anything starting with the same letter will be hashed together. As you can see, that's a lot of collisions.

Another idea is to hash according to the length of the string.

hash[len(text)] = text

You can use what hayden suggests in a comment above, and cause further collisions by taking the length modulo some number. Eg.

hash[len(text) % 5] = text

Upvotes: 0

kindall
kindall

Reputation: 184071

You could use the sum of the characters in a string. It's the first hash function I was taught back when I was first learning BASIC in high school, and I ran into the collision problem right away and had to figure out how to deal with it.

sum(ord(c) for c in text)

Transpositions are easily achieved by swapping strings or even words. For more fun you could also make it case-insensitive:

sum(ord(c) for c in text.lower())

I'll even give you a sample collision for that last one: Jerry Kindall -> Dillan Kyrjer :-)

Upvotes: 4

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